Membrane plate for plate filter presses

ABSTRACT

A membrane plate for a filter press includes a plate member composed of a plate wall having a peripheral region provided with a plate wall groove and a plate frame surrounding the plate wall. A flexible press membrane is disposed adjacent at least one side of the plate wall and a holding frame covers a membrane edge bead received in the plate wall groove. A connecting arrangement secures the holding frame to the plate frame and permits transverse movement of the holding frame with respect to the plate wall. The connecting arrangement includes a continuous peripheral groove in the plate frame and a continuous, elastic member supported on the holding frame. The elastic member projects from the holding frame and is received by the continuous peripheral groove.

BACKGROUND OF THE INVENTION

The invention relates to a membrane plate for plate filter presses, themembrane plate including a plate wall having a plate frame around itsperiphery which, together with the adjacent filter plates, delimits afilter chamber on both sides of the plate. On at least one side of theplate, the membrane plate is provided with a press membrane which can becharged by a pressure medium and is provided with a continuous edge beadthat is fixed in a groove in the transition region between the plateframe and the plate wall and is covered on its side facing the adjacentplate by a holding frame that is fastened to the plate edge so as to bemovable, within limits, in a direction perpendicular to the plane of theplate. If the filter chamber is open, the holding frame projects beyondthe plane defined by the contact surface of the filter frame.

A membrane plate of the above-mentioned type is disclosed in DE-A3,520,653 to which corresponds U.S. Pat. No. 4,749,482. Since theholding frame of the prior art membrane plate is connected with theplate frame so as to be movable in a direction perpendicular to theplate plane, the edge bead can be held loosely or only with a slighttension in the groove when the chamber is open. The material of the edgebead is thus compressed by way of the movable holding frame only if thefilter plate packet is closed. The degree of deformation is hereunequivocally determined by the dimension by which the holding frameprojects beyond the plane defined by the contact surface of the plateframe. As soon as the chamber is opened again, the material of the edgebead is able to relax again so that, during the relatively long openingtimes in operation of such a plate filter press, the material of theedge bead is able to recover. Since, moreover, the holding frame alsocovers part of the adjacent membrane edge, a sufficient seal results forthe pressure chamber disposed between the plate wall and the membranewhen the filter chamber is closed, thus permitting very high pressureforces to be exerted on the membrane. If the filter chamber is closed,the filter cloth is not pressed onto the membrane material, but only onthe much more resistant material of the holding frame so that here againthe danger of locally excessive stresses, which may constitute thestarting point for cracks, is avoided. The holding frame is fastened tothe plate frame by way of resilient snap pins.

SUMMARY OF THE INVENTION

The invention is now based on the task of further improving the priorart membrane plate by improving the connection between the pressmembrane and the membrane plate and by improving the geometricrelationships in the transition region.

This task is accomplished by the invention in that the plate frame, atits edge facing the peripheral surface of the holding frame, is providedwith a continuous groove. The holding frame is provided with aperipheral web-like projection of an elastic material which isassociated with the groove, engages therein and limits movement of theholding frame in a direction perpendicular to the plane of the plate.This configuration has the advantage, compared to the prior artconnection by way of resiliently mounted snap pins, of a considerablysimplified manufacturing process since only one continuous groove mustbe shaped into the plate frame. Since the web-like projection is made ofan elastic material, it can easily be pressed into the groove after theholding frame has been placed onto the edge bead so that the holdingframe is locked to the plate frame in a form-locking but movable manner.As a preferred feature of the invention it is here provided that atleast the holding frame is fixed to the press membrane in the region ofthe edge bead. In this connection it is further advisable for theweb-shaped projection also to be fixed to the holding frame. Since, inconsideration of the sealing effect, the press membrane as well as theweb-shaped projection must be produced of a relatively soft materialcompared to the holding frame, particularly of rubber, the holding framemust be glued to the edge of the press membrane and/or to the web-shapedprojection or it must be connected by vulcanization if the holding frameitself is made of a rubber material having a higher Shore hardness.Another advantage of the solution according to the invention compared tothe prior art is that the web-shaped projection serving as a fasteningmeans for the holding frame can also be produced of a corrosionresistant, non-metallic material so that, aside from the exceptionalcase of hot filtration, such filter plates can be produced entirely ofnon-metallic materials, particularly of plastic and/or rubber.

As a suitable feature of the invention it is provided that theperipheral surface of the holding frame is provided with a continuoussupporting web for the web-shaped projection. This arrangement has theadvantage that, in the installed position, the holding frame is held ina form lock in the plate frame by way of the web-shaped projection sothat, whether the web-shaped projection is inserted loosely or it isfixed to the holding frame, the holding frame and thus the pressmembrane are reliably held when the plate filter press is open. In thisconnection it is advisable for the web-shaped projection to be providedwith a sealing element that lies against the supporting web of theholding frame. In this way, the gap between the plate frame and theholding frame, which is required to move the holding frame, is reliablysealed. This is particularly advantageous if, as a further feature ofthe invention, the plate frame edge facing the holding frame isprovided, between the contact region of the edge bead, on the one hand,and the web-shaped projection, on the other hand, with a channel-shapedrecess that extends over at least part of the periphery and is incommunication by way of bores with the channel bores provided for thefiltrate and the washing liquid and extending within the plate frameand, if transverse bores are provided in the holding frame, forrespectively connecting the chamber with the channel-shaped recesses. Inthis way a sealed channel is provided between the plate frame and theholding frame so as to ensure proper liquid discharge in the edge regionof the filter cake. Since for most uses such filter plates are made ofplastic, the solution according to the invention has the additionaladvantage that it is possible to influence the filtrate discharge andthus the cake formation by way of the number and/or position of theexisting transverse bores with respect to the channel bores.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view, partially in section, of a membrane plateequipped with a double membrane, and of an adjacent filter plate;

FIG. 2 is a sectional view, to a larger scale, of the membrane plate ofFIG. 1 including fastening means for the press membrane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The membrane plate 1 shown in FIG. 1 for a plate filter press equippedwith vertically oriented filter plates includes a plate wall 2 which isprovided with a plate frame 3 around its periphery. Plate frame 3 hassuch a thickness that it projects beyond the two surfaces of plate wall2. Several such membrane plates 1 next to one another, or arranged toalternate with simple filter plates 18 without membranes, or alsoalternating with simple frames, together constitute the filter platepacket of a filter plate press. Depending on the configuration of thefilter press, such membrane plates may also be provided with a membraneon only one side which is a configuration that is employed, inparticular, for plate filter presses in which the filter plates areoriented horizontally. A respective filter chamber is formed betweenmembrane plate 1 and each further plate adjacent thereto.

A press membrane 4 fixed in a groove 7 in the transition region 5between plate frame 3 and plate wall 2 by means of an edge bead 6 restson each side of plate wall 2. The press membrane 4 made of an elasticmaterial, for example of rubber of an appropriate quality, is provided,on its side facing away from plate wall 2, with a plurality of nub-likeprojections 8 which support a filter cloth 9 that is placed over them.In the illustrated embodiment, the filter cloth hangs over the upperedge 10 of plate frame 3 and is provided at the respectively associatedlocations with passage openings corresponding to the channel bores 11 inthe plate frame. In the illustrated embodiment, the central region ofthe filter plate is not shown. Depending on the structure of the plateas a whole, it may have a closed surface or it may be provided with acorresponding passage fitting for a central heavy liquid discharge.However, the configuration of this region is of no significance for anunderstanding of the structure according to the invention.

As will be discussed in greater detail below with reference to theenlarged sectional view, the edge bead 6 of press membrane 4 is fastenedby means of a holding frame 12 which is held at plate frame 3 by way ofappropriate connecting means to be movable in a direction perpendicularto the plane of the plate. As evident from the illustration, filtercloth 9 covers plate frame 3 as well as holding frame 12.

As indicated in the enlarged sectional view of FIG. 2, the groove 7accommodates the edge bead 6 of press membrane 4 and lies approximatelyat the same level as the respective exterior plane 13 of plate wall 2.In the region of edge bead 6, press membrane 4 is covered by holdingframe 12 which is fastened over edge bead 6 by way of appropriatefastening means 14 that will be described in greater detail below.Fastening means 14 are configured in such a way that, if the filterchamber is open (i.e., if the associated adjacent plate, such as plate18, is spaced from membrane plate 1, as shown, for example, in FIG. 1)the fastening means press holding frame 12 onto edge bead 6 while onlyslightly compressing the edge bead. This operational state is shown inFIG. 2, and corresponds to a first position of holding frame 12, wherethe lateral surface of the holding frame projects beyond the lateralsurface 16 of plate frame 3, which serves as a contact surface betweenmembrane plate 1 and further adjacent plates. The extent to whichlateral surface 15 projects beyond lateral surface 16 is herepredetermined in such a way that the desired deformation of edge bead 6is realized when the contact surface 17 of the adjacent plate 18 ispressed onto the corresponding lateral surface 16 of membrane plate 1 sothat, with the filter chamber thus being closed, surface 15 and surface16 lie in a common plane. This operational state corresponds to a secondposition of holding frame 12. Thus, the pressure chamber 19 disposedbetween plate wall 2 and membrane 4 is sealed toward the edge, with thesealing force to be derived from the defined deformation of edge bead 6in conjunction with the given wall thickness of press membrane 4 againdetermining the highest permissible pressure force for the pressuremedium to be introduced into pressure chamber 19.

As soon as the filter chamber is opened, the edge bead is able topractically completely relax except for a slight bias. The material ofthe edge bead is able to "recover" during the duration of the openingperiod.

FIG. 2 shows to a larger scale and as a sectional view the connectingmeans for the connection between plate frame 3 and holding frame 12. Inthe illustrated embodiment, membrane 4 is made, for example, of a rubberhaving a Shore hardness 65. The associated holding frame 12 is likewisemade of a rubber which, however, has a greater hardness, for example, aShore hardness of 78. Since both elements are made of rubber, theholding frame can be fixed to the region of the edge bead 6 of membrane4 by vulcanization. If plastics are employed for holding frame andmembrane, both elements can be appropriately welded together.

On its peripheral surface facing plate frame 3, holding frame 12 is nowprovided with a continuous supporting web 32 whose outer edge extendsclosely to the peripheral surface 33 of plate frame 3 facing the holdingframe. A fastening means 14 in the form of a web-shaped projection 34made of an elastic material such as a soft rubber or plastic having ashore hardness less than that of the holding frame, now lies againstthis supporting web 32. In the region of holding frame 12, thisprojection widens to form a sealing element 35 which fills the gapbetween the exterior peripheral surface of holding frame 12 and theinterior peripheral surface of plate frame 3. The outer edge of theweb-shaped projection 34 here lies in a continuous groove 36 in theinterior peripheral surface 33 of plate frame 3. After membrane 4 hasbeen inserted, the sealing element 35 of web-shaped projection 34 cannow be pressed, together with holding frame 12 fixed to it, into groove36 from the outside. In embodiments in which the sealing element 35 ofthe web-shaped projection is fixed to the holding frame, slightdeformation of the web-shaped projection 34 of the holding frame in theplane of the plate permits the holding frame to engage inwardly in thegroove. The web-shaped projection 34, which serves to fasten plate frame3 and holding frame 12 is here dimensioned in such a way that edge bead6, when engaged as shown in FIG. 2, is compressed very slightly.Fastening means 14, together with continuous supporting web 32 andcontinuous groove 36, constitute a connecting means for connecting theholding frame to the plate frame, and for limiting the transversemovement of the holding frame between its first position and its secondposition, as described above. The elasticity of web-shaped projection 34ensures mobility of holding frame 12 so that, if the filter chamber isclosed, the lateral surface 15 defined by holding frame 12 can bepressed down so as to be in a common plane with lateral surface 16defined by the plate frame while simultaneously deforming edge bead 6.This causes edge bead 6, which has a smaller cross section than groove7, to be shaped into groove 7, producing an extremely effective sealthat is able to withstand pressure forces of more than 10 bar for therear side of the press membrane, that is, the side facing pressurechamber 19.

As is evident from the sectional view, press membrane 4 is provided,adjacent edge bead 6, with a continuous bulge 27 that is oriented towardthe filter chamber; a corresponding continuous bulge 28 in plate wall 2is associated with each bulge 27.

As can be seen in FIG. 2, if pressure chamber 19 is charged with apressure medium, the press membrane 4 is pushed into the associatedfilter chamber area. To reduce stretching of the membrane material inthe peripheral region of membrane 4, which is already under great strainfrom the stresses created by the clamping forces, the apical region ofbulge 27, on the side facing the associated filter chamber, is providedwith a continuous supporting bead 30 that extends parallel to the inneredge of holding frame 12. If, during the pressing process, the pressmembrane is subjected fully to pressure medium and is pushed far intothe associated filter chamber, then, approximately at the moment atwhich portions of the press membrane in the vicinity of plate 2 areparallel to plate 2, the supporting bead 30 comes into contact with theinner edge of holding frame 12 and thus limits movement of membrane 4 inthis region. The further deformation of the press membrane underprogressive compression then takes place at an even greater distancefrom the fastening edge of the press membrane so that, as a whole,critical stresses on the press membrane are avoided in its particularlyvulnerable peripheral region.

However, supporting bead 30 need not be continuous. As shown in FIG. 1,bead 30 may be interrupted at regular uniform intervals by grooves 31that are oriented radially to the plate edge. These grooves 31 areassociated with approximately coaxially oriented bores 37 in holdingframe 12 which, as shown in the sectional view of FIG. 2, open into acontinuous channel-like recess 38 in the peripheral region of membrane4. Grooves 31 and bores 37 serve to permit extraction of liquid in theperipheral region of the membrane as well and thus serve to ensure thatthe filter cake is pressed out almost completely, as the recesses 38 arein communication with channel bores 11 by way of corresponding,non-illustrated bores in plate frame 3 in the region of the channelbores.

I claim:
 1. In a membrane plate to be assembled with additional platesto form a filter press, the membrane plate comprisinga plate membercomposed of a plate wall having a peripheral region provided with aplate wall groove, and a plate frame surrounding said plate wall at saidperipheral region; said plate frame having a plate frame lateral surfaceextending in a plane substantially parallel to and directed away from aplane of said plate wall, and a plate frame interior peripheral surfacefacing in a direction of said plate wall and being oriented generallyperpendicularly to the plane of said plate frame lateral surface; aflexible press membrane disposed adjacent at least one side of saidplate wall to be acted upon by a pressure medium, said membrane having acontinuous peripheral edge bead and being seated in said plate wallgroove; a holding frame covering said edge bead on a side of said edgebead directed away from said plate wall, said holding frame having aholding frame exterior peripheral surface facing toward said plate frameinterior peripheral surface; and connecting means for securing saidholding frame to said plate frame and for permitting movement of saidholding frame in a direction perpendicular to the plane of said platewall between first and second positions; in said first position saidholding frame being closer to said wall plate groove than in said secondposition; the improvement wherein said connecting means comprisesacontinuous peripheral groove in said plate frame interior peripheralsurface; a continuous, elastic member supported on said holding frameexterior peripheral surface; said elastic member comprising acontinuous, elastic web projecting from said holding frame exteriorperipheral surface and being received by said continuous peripheralgroove; securing means for securing said elastic member to said holdingframe and wherein said membrane and said elastic member are formed of anelastomeric material having a shore hardness less than a shore hardnessof said holding frame.
 2. The membrane plate according to claim 1,wherein said securing means includes a continuous supporting shoulderprovided on said holding frame and adjoining said holding frame exteriorperipheral surface; said supporting shoulder engaging said elasticmember.
 3. The membrane plate according to claim 2, wherein said elasticmember includes a sealing element extending from said holding frameexterior peripheral surface to said plate frame interior peripheralsurface, said sealing element abutting against said supporting shoulder.4. The membrane plate according to claim 3, further comprisinga firstchannel extending along said plate frame and being bounded by a surfaceof said edge bead of said press membrane, said plate frame interiorperipheral surface and a surface of said holding frame; a second channelpassing through said plate frame and being in communication with saidfirst channel; and a third channel passing through said holding frameand having opposite first and second ends; said first end opening intosaid first channel and said second end opening into a space adjacentsaid press membrane.
 5. The membrane plate according to claim 1, whereinsaid holding frame is firmly affixed to said press membrane at a regionadjacent said edge bead.
 6. The membrane plate according to claim 1,wherein said securing means comprises means for firmly affixing saidelastic member to said holding frame.